Study On The Design Of Transition Metal Based Catalyst With Rich Vacancy And Their Electrochemical Nitrogen Fixation Performance

Ammonia,as a chemical feedstock for the synthesis of reactive nitrogen compounds,is essential for life on Earth.In recent years,electrochemical nitrogen reduction reaction（ENRR）has attracted a lot of attention as an economical and efficient new way to produce ammonia.However,the efficiency of electrocatalytic ammonia synthesis still needs to be further improved.Therefore,the development and construction of novel ENRR catalysts with high efficiency,stability and cost saving is the core focus of promoting the development of nitrogen fixation technology.In view of this,this paper starts from the design of electrocatalyst structure to increase the number of active sites,and successfully synthesizes a noval and efficient transition metal-based nanomaterials.Through a series of characterization techniques and performance tests,the phase composition,morphology and electrochemical properties of the catalyst were studied in detail.The main contents are as follows:（1）Based on the interface-engineering strategy,a single-layer 1T-type MoS₂（SV-1T-MoS₂）composite catalyst with a large number of S vacancy was synthesized on the MoO₃ nanoribbons substrate（SV-1T-MoS₂@MoO₃）.This catalyst was constructed for the first time and applied to the research field of electrochemical nitrogen fixation.Compared with the related MoS₂ based ENRR catalyst previously reported,SV-1T-MoS₂@MoO₃ showed a higher ammonia yield(116.1μg h^-1 mg^-1_cat.)and Faraday efficiency（18.9%）.The experimental results imply that the existence of S vacancy is beneficial to exposuring more Moatoms,and increasing the adsorption capacity and conversion rate of N₂.Meanwhile,the composite materials with 2 layers and N layers of SV-1T-MoS₂ were designed for comparison,and the results show that the material with single-layer structure possesses the best nitrogen catalytic capacity.Combined with density functional theory（DFT）calculations,it is confirmed that the construction of the composite structure is conducive to the transfer of electrons from the substrate MoO₃ to the MoS₂ layer,and promotes the reaction in a more favorable direction for ENRR.In addition,compared with the pure MoS₂ with S vacancy,the rate-determining step of SV-1T-MoS₂@MoO₃（*NN→*NNH）has a lower energy barrier,which greatly improves the efficiency of ENRR.（2）Ultrathin vanadium oxide nanoribbon(VO-VO_0.9 NRs)with oxygen vacancy was synthesized by hydrothermal synthesis and low temperature calcination.The morphology has a large specific surface area,which can provide more active sites for chemical adsorption of nitrogen,and the oxygen vacancy acts as an effective reactive active site in ENRR process.Compared with VO NRs,it exhibits better nitrogen reduction ability(59.9μg h^-1 mg^-1_cat.,8.84%).At the same time,the catalyzed electrolyte solution was detected without the presence of by-products,which means that Vo-VO_0.9 NRs has good selectivity.In addition,the excellent chemical stability of VO-VO_0.9 NRs was confirmed by six consecutive cycle tests and 30 hours of long-term constant voltage tests.In summary,this paper provides a new reference for the design of transition metal-based catalysts applied to ENRR.